Tri-mixed alkylsulfonium salts of N-phosphonomethylglycine and their use as plant growth regulators and herbicides

ABSTRACT

Novel tri-mixed alkylsulfonium salts of N-phosphonomethylglycine are disclosed herein, having the formula ##STR1## in which R 1 , R 2 , and R 3  represent C 1  -C 6  alkyl and n is zero or one, wherein no more than two of R 1 , R 2 , or R 3  are identical. The compounds are useful in regulating the natural growth or development of plants and as herbicides.

CROSS REFERENCE TO RELATED APPLICATION

This is a continuation-in-part of application Ser. No. 212,921, filedDec. 4, 1980, now U.S. Pat. No. 4,315,765.

BACKGROUND OF THE INVENTION

This invention is directed to novel chemical compounds and their use inregulating the natural growth or development of plants. In particular,this invention relates to the chemical treatment of plants to altertheir natural growth or development for the purpose of enhancing variousagricultural or horticultural features of the plants, and also to thecontrol of undesirable vegetation.

It is well known among those skilled in the art of agriculture andhorticulture that various features of plant growth can be modified orregulated to produce a variety of beneficial effects.

For instance, certain types of treatment can produce defoliation of aplant in a beneficial manner, i.e., inhibiting further leaf growth whilepermitting further development of the productive plant parts. As aresult, the productive parts demonstrate extra growth, and subsequentharvesting operations are facilitated. Defoliants are particularlyuseful in flax, cotton, and bean crops, and other crops of a similarnature. Although defoliation results in the killing of leaves, it is nota herbicidal action per se since the remainder of the plant is unharmed.Indeed, killing of the treated plant is undesirable when defoliation issought, since leaves will continue to adhere to a dead plant.

Another response demonstrated by plant growth regulants is the generalretardation of vegetative growth. This response has a wide variety ofbeneficial features. In certain plants it causes a diminution orelimination of the normal apical dominance, and thus leads to a shortermain stem and increased lateral branching. This alteration of thenatural growth or development produces smaller, bushier plants whichoften demonstrate increased resistance to drought and pest infestation.The retardation of vegetative growth in turf grasses is particularlydesirable. When the vertical growth rate of such grasses is lessened,root development is enhanced and a denser, sturdier turf is produced.The retardation of turf grasses also serves to increase the intervalbetween mowings of lawns, golf courses and similar grassy areas.

In many types of plants, such as silage crops, potatoes, sugar cane,beets, grapes, melons and fruit trees, the retardation of vegetativegrowth results in an increase in the carbohydrate content of the plantsat harvest. It is believed that the retardation or suppression of suchgrowth at the appropriate stage of development causes less of theavailable carbohydrate to be consumed for vegetative growth and resultsin an enhanced starch and/or sucrose content. Retardation of vegetativegrowth in fruit trees is demonstrated by shorter branches and greaterfullness of shape, and often results in lesser vertical elongation.These factors contribute to the ease of access to the orchard andsimplify the fruit harvesting procedure.

BRIEF DESCRIPTION OF THE INVENTION

It has now been discovered that novel tri-mixed alkylsulfonium salts ofN-phosphonomethylglycine are useful in both regulating the naturalgrowth or development of plants and in controlling undesirablevegetation. These salts have the formula ##STR2## where R₁, R₂, and R₃represent C₁ -C₆ alkyl, and n is zero or one, wherein no more than twoof R₁, R₂ or R₃ are identical. Preferably, R₁, R₂, and R₃ each representC₁ -C₄ alkyl, wherein no more than two of R₁, R₂ or R₃ are identical.

This invention further relates to a method of regulating the naturalgrowth or development of plants comprising applying to said plants aneffective, plant-regulating, non-lethal amount of the above compounds,as well as a method of controlling undesirable vegetation comprisingapplying a herbicidally effective amount of the compounds to suchvegetation when the latter is in a postemergence state.

As employed herein, the term "natural growth or development" designatesthe normal life cycle of a plant in accordance with its genetics andenvironment, in the absence of artificial external influences. Apreferred utility of the instant compounds is in increasing the sourceyield of field grown sugarcane and sorghum. The term "regulating" isused herein to denote the bringing about through chemical means of anytemporary or permanent modification or variation from the normal lifecycle short of killing the plant.

The term "herbicidally effective amount" designates any amount of thecompounds disclosed herein which will kill a plant or any portionthereof. By "plants" is meant germinant seeds, emerging seedlings, andestablished vegetation, including roots and above-ground portions.Herbicidal effects include killing, defoliation, desiccation, stunting,leaf burn, and dwarfing. Herbicidal effects are generally achieved athigher application rates than growth regulating effects.

The term "alkyl" is used herein to include both straight-chain andbranched-chain alkyl groups. The carbon atom range is intended to beinclusive of its upper and lower limits; for example, methyl, ethyl,n-propyl, isopropyl, butyl, n-butyl, sec.-butyl, pentyl, isopentyl,neopentyl, sec.-pentyl, hexyl, isohexyl, sec.-hexyl, and the like.Hence, the term "tri-mixed alkyl" represents alkyl substitutions inwhich the sulfonium cation contains three alkyl moieties. However, nomore than two of said alkyl moieties are identical.

Examples of specific compounds falling within the above formula are:

diethylmethyl sulfonium salt of N-phosphonomethylglycine

dimethylethyl sulfonium salt of N-phosphomethylglycine

diethylisopropyl sulfonium salt of N-phosphonomethylglycine

diethyl-n-butyl sulfonium salt of N-phosphonomethylglycine

di-n-butylmethyl sulfonium salt of N-phosphomethylglycine

dimethyl-n-butyl sulfonium salt of N-phosphonomethylglycine

dimethylisopropyl sulfonium salt of N-phosphonomethylglycine

DETAILED DESCRIPTION OF THE INVENTION

In accordance with the instant invention, regulation of the naturalgrowth or development of plants is achieved by the direct application ofa compound within the above formula or a formulation of such a compoundto the plants or to any of their above-ground portions at approximately4 to 10 weeks prior to harvest. With properly controlled application, agrowth regulating effect can be achieved without herbicidal results. Theamount which constitutes an effective amount varies not only with theparticular material selected for treatment, but also with the regulatoryeffect to be achieved, the species of plant being treated and its stageof development, and whether a permanent or transient effect is sought.Other factors which bear upon the determination of an appropriate plantregulating amount include the manner of application and weatherconditions such as temperature or rainfall. Growth regulation may arisefrom the effect of the compound on either the physiological processes orthe morphology of the plant, or from both in combination or in sequence.Morphological changes are generally noticeable by observable changes inthe size, shape, color or texture of the treated plant or any of itsparts, as well as in the quantity of fruit or flowers produced.

Changes in physiological processes, on the other hand, occur within thetreated plant and are usually hidden from the eye of an observer.Changes of this type most often occur in the production, location,storage or use of chemicals naturally occurring in the plant, such ashormones. Physiological changes may be visually detectable when followedby a change in morphology. In addition, numerous analytical proceduresfor determining the nature and magnitude of changes in the variousphysiological processes are known to those skilled in the art.

The compounds of the instant invention serve to regulate the naturalgrowth or development of treated plants in a number of diverse ways, andit is to be understood that each compound may not produce identicalregulatory effects on each plant species or at every rate ofapplication. As stated above, responses will vary in accordance with thecompound, the rate, the plant, etc.

Herbicidal effects are achieved in a similar manner, and the strength ofthe application can be varied to achieve the desired result.

The compounds of this invention are readily prepared fromN-phosphonomethylglycine by reacting the latter with silver oxide toform the silver salt or with sodium hydroxide to form the sodium salt,and treating either the silver or sodium salt with a trialkylsulfoniumor -sulfoxonium halide. Alternatively, the glycine can be reacteddirectly with the trialkylsulfonium or -sulfoxonium halide in thepresence of propylene oxide. N-Phosphonomethylglycine is a commerciallyavailable material known by the common name "glyphosate." It can beprepared by the phosphonomethylation of glycine, the reaction of ethylglycinate with formaldehyde and diethylphosphite, or the oxidation ofthe N-phosphinomethylglycine. Such methods are described in U.S. Pat.No. 3,799,758 (Franz, Mar. 26, 1974).

As illustrated in the examples which follow, the compounds of theinvention can either regulate the natural growth or development ofplants or kill weeds. While regulatory responses are often desirable intheir own right, their effect on crop economics is most often of primarysignificance. Thus, increases in the yield of individual plants,increases in the yield per unit area, and reductions in the cost ofharvesting and/or subsequent processing are all to be considered inassessing the consequence of an individual regulatory effect during thegrowth or development of a plant.

The specific examples which follow are presented as merely illustrative,non-limiting demonstrations of the preparation of the compounds of theinstant invention and of their effectiveness in regulating the growth ofplants and in controlling undesirable vegetation.

EXAMPLE 1 Di-n-butylmethyl sulfonium Salt of N-phosphonomethylglycine

A reaction vessel was charged with 50 milliliters (ml) of water, 5.1grams (g) (0.03 mole) of N-phosphonomethylglycine, and 8.65 g (0.03mole) of di-n-butylmethyl sulfonium iodide. The vessel was additionallycharged with 2.2 g (0.0375 mole) of propylene oxide. The entire reactionmixture was allowed to stand at room temperature overnight. At the endof this time, the reaction mixture was extracted three times withdiethyl ether and phase separated. The aqueous phase was stripped,yielding 11.1 g. This product was triturated with tetrahydrofuran (2×10ml), then once with 10 ml acetone and stripped to yield 11.0 g ofproduct. This product was further triturated with 20 ml of acetone andthen with 10 ml diethyl ether and stripped. There was obtained a lowmelting solid, yield 9.8 g. The molecular structure of the product wasconfirmed by proton-nuclear magnetic resonance as the title compound.

EXAMPLE II Diethylmethyl sulfonium Salt of N-phosphonomethylglycine

In a similar procedure as Example I, 50 ml of water, 6.76 g (0.04 mole)of N-phosphonomethylglycine, 9.3 g (0.04 mole) of diethylmethylsulfonium iodide and 2.9 g (0.05 mole) of propylene oxide were reactedovernight at room temperature, extracted 3 times with diethyl ether andthe aqueous phase stripped of volatile (yield 12.3 g). After triturationwith acetone and diethyl ether and stripping of volatiles, there wasobtained 12.0 g of the title compound (decomposes at 60°-65° C.). Themolecular structure of the product was confirmed by proton-nuclearmagnetic resonance as that of the title compound.

EXAMPLE III Dimethylisopropyl sulfonium Salt of N-phosphonomethylglycine

In a similar procedure as Example I, 50 ml of water, 6.76 g (0.04 mole)of N-phosphonomethylglycine, 9.3 g (0.04 mole) of dimethylisopropylsulfonium iodide and 3.5 g (0.06 mole) of propylene oxide were reactedovernight at room temperature, extracted 2 times with diethyl ether andthe aqueous phase stripped (yield 11.8 g). After trituration withacetone (2 times, 10 ml each) the product was stripped again to yield11.2 g, n_(D) ³⁰ 1.5232. The molecular structure of the product wasconfirmed by proton nuclear magnetic resonsance as that of the titlecompound.

EXAMPLE IV Dimethyl-n-butyl sulfonium Salt of N-phosphonomethylglycine

In a similar procedure as Example I, 50 ml of water, 6.8 g (0.04 mole)of N-phosphonomethylglycine, 10.0 g (0.04 mole) of dimethyl-n-butylsulfonium iodide and 3.5 g (0.06 mole) of propylene oxide were reactedovernight at room temperature, extracted 2 times with diethyl ether,phase separated, and stripped of volatiles (yield 12.4 g). Aftertrituration with acetone (2 times, 10 ml each) and stripping, there wasobtained 12.9 g of a hygroscopic white solid. The molecular structure ofthe product was confirmed by proton-nuclear magnetic resonance as thetitle compound.

Other compounds within the scope of the generic formula shown above canbe prepared by either of these methods with appropriate startingmaterials.

This example demonstrates the post-emergence herbicidal activity of thecompounds prepared in Examples I and II.

Aluminum planting flats measuring 15.2×22.9×8.9 cm were filled to adepth of 7.6 cm with loamy sand soil, containing 50 parts per million(ppm) each of the commercial fungicidecis-N[(trichloromethyl)thio]-4-cyclohexene-1,2-dicarboximide (Captan®)and 17--17--17 fertilizer (percentages of N--P₂ O₅ --K₂ O) on a weightbasis). Several rows were impressed across the width of each flat and avariety of seeds of both grass and broadleaf weed species were planted,one species per row. The weed species used are listed below:

    ______________________________________                                        Grasses:                                                                      A. Yellow nutsedge  Cyperus esculentus                                        B. Foxtail          Setaria sp.                                               C. Watergrass       Echinochloa crusgalli                                     D. Wild oat         Avena fatua                                               Broadleaf weeds:                                                              E. Curly dock       Rumex crispus                                             F. Annual morning glory                                                                           Ipomoea purpurea                                          G. Velvetleaf       Abutilon theophrasti                                      H. Mustard          Brassica sp.                                              ______________________________________                                    

The broad leaf species were seeded first, and the grasses were seededfour days later. Ample seeds of each species were planted to produce 20to 50 seedlings per row after emergence, depending on the size of eachplant.

Ten days after the grasses were seeded, the emerged seedlings of allspecies were sprayed with aqueous solutions of the test compounds. Thesolutions were prepared to such dilutions that a spray rate of 80gallons per acre (750 liters per hectare) gave 4.0 pounds of testcompound per acre (4.48 kilograms per hectare) as desired for the test.Additional control flats not treated at all were used as standards forcomparison to measure the extent of weed control in the treated flats.

Nineteen days later, the test flats were compared to the standards andthe weeds in each row were rated visually in terms of percent controlranging from 0% to 100%, with 0% representing the same degree of growthas the same row in the standard and 100% representing complete kill ofall weeds in the row. All types of plant injury were taken intoconsideration. The results are shown in Table I.

                                      TABLE I                                     __________________________________________________________________________    HERBICIDAL TEST RESULTS                                                                         Percent Control                                                        Application                                                                          Grass Weeds                                                                            Broadleaf Weeds                                    Test Compound                                                                            Rate (lb/A)                                                                          A B  C D E F G  H                                           __________________________________________________________________________    N--phosphonomethyl-                                                                      4.0    70                                                                              100                                                                              90                                                                              90                                                                              80                                                                              50                                                                              80 75                                          glycine, di-n-butyl                                                           methyl sulfonium salt                                                         N--phosphonomethyl-                                                                      4.0    75                                                                              90 90                                                                              60                                                                              60                                                                              55                                                                              65 50                                          glycine, diethylmethyl                                                        sulfonium salt                                                                __________________________________________________________________________

METHODS OF APPLICATION

Whether used as plant growth regulators or as herbicides, the compoundsof the present invention are most useful when applied directly to theplants subsequent to their emergence from the soil. In use at anagricultural field site, the compounds are generally embodied insuitable formulations containing additional ingredients and diluentcarriers to aid in their dispersal. Examples of such ingredients orcarriers are water, organic solvents, dusts, granules, surface activeagents, water-in-oil and oil-in-water emulsions, wetting agents,dispersing agents, and emulsifiers. The formulations generally take theform of dusts, solutions, emulsifiable concentrates, or wettablepowders.

A. DUSTS

Dusts are dense powder compositions which combine the active compoundswith a dense, free-flowing solid carrier. They are intended forapplication in dry form and are designed to settle rapidly to avoidbeing windborne to areas where their presence is not desired.

The carrier may be of mineral or vegetable origin, and is preferably anorganic or inorganic powder of high bulk density, low surface area, andlow liquid absorptivity. Suitable carriers include micaceous talcs,pyrophyllite, dense kaolin clays, tobacco dust, and ground calciumphosphate rock.

The performance of a dust is sometimes aided by the inclusion of aliquid or solid wetting agent, of ionic, anionic, or nonionic character.Preferred wetting agents include alkylbenzene and alkylnaphthalenesulfonates, sulfated fatty alcohols, amines or acid amides, long chainacid esters of sodium isothionate, esters of sodium sulfosuccinate,sulfated or sulfonated fatty acid esters, petroleum sulfonates,sulfonated vegetable oils, and ditertiary acetylenic glycols.Dispersants are also useful in the same dust compositions. Typicaldispersants include methyl cellulose, polyvinyl alcohol, ligninsulfonates, polymeric alkylnaphthalene sulfonates, sodium naphthalenesulfonate, polymethylene bisnaphthalenesulfonate, andsodium-N-methyl-N-(long chain acid) taurates.

In addition, inert absorptive grinding aids are frequently included indust compositions to aid in the manufacturing of the dust. Suitablegrinding aids include attapulgite clay, diatomaceous silica, syntheticfine silica and synthetic calcium and magnesium silicates.

In typical dust compositions, carriers are usually present inconcentrations of from about 30 to 90 weight percent of the totalcomposition. The grinding aid usually constitutes about 5 to 50 weightpercent, and the wetting agent up to about 1.0 weight percent.Dispersants, when present, constitute up to about 0.5 weight percent,and minor amounts of anticaking and antistatic agents may also bepresent. The particle size of the entire composition is usually about 30to 50 microns.

B. SOLUTIONS

Aqueous solutions of the active compounds are prepared such thatapplication at the rate of about 1 to about 200 gallons of solution peracre (about 9 to about 1875 liters per hectare) will provide therequired amount of active ingredient. A small amount of non-phytotoxicsurfactant typically between 0.05% and 0.5% by weight is usuallyincluded to improve the wetting ability of the solution and thus itsdistribution over the plant surface. Anionic, cationic, nonionic,ampholytic, and zwitterionic surfactants are all useful in this regard.

Suitable anionic surfactants include alkali metal, ammonium, and aminesalts of fatty alcohol sulfates having from 8-8 carbon atoms in thefatty chain and sodium salts of alkyl benzene sulfonates having from 9to 15 carbon atoms in the alkyl chain. Suitable cationic surfactantsinclude dimethyl dialkyl quaternary ammonium halides with alkyl chainsof 8 to 18 carbon atoms. Suitable nonionic surfactants includepolyoxyethylene adducts of fatty alcohols having 10 to 18 carbon atoms,polyethylene oxide condensates of alkyl phenols with alkyl chains of 6to 12 carbon atoms and 5 to 25 moles of ethylene oxide condensed ontoeach mole of alkyl phenol, and polyethylene oxide condensates ofsorbitan esters with 10 to 40 moles of ethylene oxide condensed ontoeach mole of sorbitan ester. Suitable ampholytic surfactants includesecondary and tertiary aliphatic amine derivatives with one aliphaticsubstituent containing 8 to 18 carbon atoms and another containingcontaining an anionic water-solubilizing group such as a sulfate orsulfonate. Sodium-3-dodecylaminopropionate and sodium-3-dodecyl aminopropane sulfonate are examples. Suitable zwitterionic surfactantsinclude derivatives of aliphatic quaternary ammonium compounds with onealiphatic substituent containing 8 to 18 carbon atoms and anothercontaining an anionic water-solubilizing group. Examples of are3-(N,N-dimethyl-N-hexadecylammonio)propane-1-sulfonate and3-(N,N-dimethyl-N-hexadecylammonio)-2-hydroxy propane-1sulfonate.

C. EMULSIFIABLE CONCENTRATES

Emulsifiable concentrates are solutions in which the active materialsand an emulsifying agent are dissolved in a non-watermiscible solvent.Prior to use, the concentrate is diluted with water to form a suspendedemulsion of solvent droplets.

Typical solvents for use in emulsifiable concentrates include weed oils,chlorinated hydrocarbons, and non-water-miscible ethers, esters, andketones.

Typical emulsifying agents are anionic or nonionic surfactants, ormixtures of the two. Examples include long-chain mercaptan polyethoxyalcohols, alkylaryl polyethoxy alcohols, sorbitan fatty acid esters,polyoxyethylene ethers with sorbitan fatty acid esters, polyoxyethyleneglycol esters with fatty or rosin acids, fatty alkylol amidecondensates, calcium and amine salts of fatty alcohol sulfates,oil-soluble petroleum sulfonates, or preferably mixtures of theseemulsifying agents. Such emulsifying agents usually comprise about 1 to10 weight percent of the total composition.

Typical emulsifiable concentrates contain about 15 to 50 weight percentactive material, about 40 to 82 weight percent solvent, and about 1 to10 weight percent emulsifier. Other additives such as spreading agentsand stickers can also be included.

D. WETTABLE POWDERS

Wettable powders are water-dispersible compositions containing theactive material, an inert solid extender, and one or more surfactants toprovide rapid wetting and prevent flocculation when suspended in water.

Suitable solid extenders include both natural minerals and materialsderived synthetically from such minerals. Examples include kaolinites,attapulgite clay, montmorillonite clays, synthetic silicas, syntheticmagnesium silicate and calcium sulfate dihydrate.

Suitable surfactants include both nonionic and anionic types, andfunction as wetting agents and dispersants. Usually one of each isincluded. Preferred wetting agents are alkylbenzene and alkylnaphthalenesulfonates, sulfated fatty alcohols, amines or acid amides, long chainacid esters of sodium isothionate, esters of sodium sulfosuccinate,sulfated or sulfonated fatty acid esters, petroleum sulfonates,sulfonated vegetable oils, and ditertiary acetylenic glycols. Preferreddispersants are methyl cellulose, polyvinyl alcohol, lignin sulfonates,polymeric alkylnaphthalene sulfonates, sodium naphthalene sulfonate,polymethylene bisnaphthalenesulfonate, and sodium-N-methyl-N(long chainacid) taurates.

Typical wettable powders contain 25 to 90 percent active material, 0.5to 2.0 percent wetting agent, 0.25 to 5.0 percent dispersant, and from9.25 to 74.25 weight percent inert extender. Frequently, 0.1 to 1.0percent of the extender is replaced by a corrosion inhibitor and/or anantifoaming agent.

E. IN GENERAL

In general, any conventional postemergence method of application can beused, including common dusting or spraying equipment. The amount ofactive ingredient which is effective in producing the desired result, beit herbicidal or growth-regulating, depends on the nature of the plantspecies to be controlled and the prevailing conditions. Herbicidaleffects are usually achieved at 0.1 to 50 pounds active ingredient peracre, preferably 1 to 10, while plant growth regulation is usuallyachieved at 0.1 to 20 pounds active ingredient per acre, preferably 0.5to 5. It will be readily apparent to one skilled in the art thatcompounds of lower activity will require a higher dosage than moreactive compounds for the same degree of control.

What is claimed is:
 1. A compound having the formula ##STR3## whereinR₁, R₂, and R₃ represent C₁ -C₆ alkyl, and n is zero or one, wherein nomore than two of R₁, R₂ or R₃ are identical.
 2. The compound accordingto claim 1 in which n is zero.
 3. The compound according to claim 2 inwhich R₁, R₂ and R₃ each represent C₁ -C₄ alkyl.
 4. The compoundaccording to claim 2 in which R₁ and R₂ are each n-butyl and R₃ ismethyl.
 5. The compound according to claim 2 in which R₁ and R₂ are eachethyl and R₃ is methyl.
 6. The compound according to claim 2 in which R₁and R₂ are each methyl and R₃ is isopropyl.
 7. The compound according toclaim 2 in which R₁ and R₂ are each methyl and R₃ is n-butyl.
 8. Anherbicidal composition comprising an herbicidally effective amount of acompound having the formula ##STR4## where R₁, R₂, and R₃ represent C₁-C₆ alkyl, and n is zero or one, wherein no more than two of R₁, R₂ orR₃ are identical, and an inert diluent carrier.
 9. An herbicidalcomposition according to claim 8 in which n is zero.
 10. An herbicidalcomposition according to claim 9 in which R₁, R₂ and R₃ each representC₁ -C₄ alkyl.
 11. An herbicidal composition according to claim 9 inwhich R₁ and R₂ are each n-butyl and R₃ is methyl.
 12. An herbicidalcomposition according to claim 9 in which R₁ and R₂ are each ethyl andR₃ is methyl.
 13. An herbicidal composition according to claim 9 inwhich R₁ and R₂ are each methyl and R₃ is isopropyl.
 14. An herbicidalcomposition according to claim 9 in which R₁ and R₂ are each methyl andR₃ is n-butyl.
 15. A method of controlling undesirable vegetationcomprising applying to the vegetative in post-emergent state anherbicidal composition comprising an herbicidally effective amount of acompound having the formula ##STR5## where R₁, R₂, and R₃ represent C₁-C₆ alkyl, and n is zero or one, wherein no more than two of R₁, R₂ orR₃ are identical, and an inert diluent carrier.
 16. The method accordingto claim 15 in which n is zero.
 17. The method according to claim 16 inwhich R₁, R₂ and R₃ each represent C₁ -C₄ alkyl.
 18. The methodaccording to claim 16 in which R₁ and R₂ are each n-butyl and R₃ ismethyl.
 19. The method according to claim 16 in which R₁ and R₂ are eachethyl and R₃ is methyl.
 20. The method according to claim 16 in which R₁and R₂ are each methyl and R₃ is isopropyl.
 21. The method according toclaim 16 in which R₁ and R₂ are each methyl and R₃ is n-butyl.
 22. Amethod of controlling undesirable vegetation in the post-emergent stateby applying to the vegetation a post-emergent herbicidally effectiveamount of a tri-mixed alkylsulfonium salt of N-phosphonomethylglycinewherein said alkyl groups each contain from 1 to 6 carbon atoms andwherein no more than two of said alkyl groups are identical.
 23. Themethod of claim 22 wherein said alkyl groups each contain 1 to 4 carbonatoms and no more than two of said alkyl groups are identical.
 24. Amethod of controlling undesirable vegetation in the post-emergent stateby applying to the vegetation a post-emergence herbicidally effectiveamount of a tri-mixed alkylsulfoxonium salt of N-phosphonomethylglycinewherein said alkyl groups each contain from 1 to 6 carbon atoms andwherein no more than two of said alkyl groups are identical.
 25. Themethod of claim 24 wherein said alkyl groups each contain 1 to 4 carbonatoms and no more than two of said alkyl groups are identical.
 26. Anherbicidal composition comprising a post-emergent herbicidally effectiveamount of a tri-mixed alkylsulfonium salt of N-phosphonomethylglycinewherein said alkyl groups each contain from 1 to 6 carbon atoms andwherein no more than two of said alkyl groups are identical, and aninert diluent carrier.
 27. The method of claim 26 wherein said alkylgroups each contain 1 to 4 carbon atoms and no more than two of saidalkyl groups are identical.
 28. An herbicidal composition comprising apost-emergence herbicidally effective amount of a tri-mixedalkylsulfoxonium salt of N-phosphonomethylglycine wherein said alkylgroups each contain from 1 to 6 carbon atoms and wherein no more thantwo of said alkyl groups are identical, and an inert diluent carrier.29. The method of claim 28 wherein said alkyl groups each contain 1 to 4carbon atoms and no more than two of said alkyl groups are identical.30. Compounds corresponding to tri-mixed alkylsulfonium salts ofN-phosphonomethylglycine according to claim 1 wherein said alkyl groupseach contain from 1 to 6 carbon atoms and wherein no more than two ofsaid alkyl groups are identical.
 31. Compounds of claim 30 wherein saidalkyl groups each contain 1 to 4 carbon atoms and no more than two ofsaid alkyl groups are identical.
 32. Compounds corresponding totri-mixed alkylsulfoxonium salts of N-phosphonomethylglycine accordingto claim 1 wherein said alkyl groups each contain from 1 to 6 carbonatoms and wherein no more than two of said alkyl groups are identical.33. Compounds of claim 32 wherein said alkyl groups each contain 1 to 4carbon atoms and no more than two of said alkyl groups are identical.